Transformer-Coupled LC-VCO Layout for Lower Phase Noise
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Solution Overview
Problem
Inductance-capacitance voltage controlled oscillators (LC-VCOs) face challenges in achieving low phase noise while maintaining low power consumption, primarily due to single-ended parasitic capacitance.
Innovation Solution
The design incorporates a transformer-based VCO configuration with a majority of the total capacitance coupled to the secondary stage, preventing single-ended capacitance from affecting the gain stage and utilizing a capacitor bank with switched capacitors and varactors to reduce phase noise and adjust resonant frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If single-ended capacitance is used in LC-VCO design, then circuit simplicity is maintained, but phase noise increases significantly
Solution Approach 1:
The patent divides the capacitance into two distinct components: a first capacitance connected to the gain stage and a second capacitance connected to the tank circuit. This segmentation allows the second capacitance to be optimized for low phase noise while the first capacitance handles gain stage requirements, thereby reducing overall phase noise without significantly increasing circuit complexity.
Solution Approach 2:
The patent extracts the problematic single-ended capacitance from the gain stage and relocates it to the tank circuit. By taking out the capacitance that causes phase noise and placing it where it belongs (in the tank circuit), the gain stage is relieved of the harmful capacitive loading, resulting in significantly reduced phase noise.
2Adaptability or versatility
If capacitance is increased to lower resonant frequency, then frequency tuning range is improved, but phase noise increases
Solution Approach 1:
The patent segments the total capacitance into two parts: a first capacitance for frequency tuning and a second capacitance for phase noise optimization. This allows independent optimization of each component - the first capacitance can be varied for wide frequency tuning while the second capacitance is optimized to minimize phase noise, resolving the contradiction between tuning range and phase noise.
Solution Approach 2:
The patent applies different quality requirements to different parts of the capacitance system. The first capacitance is optimized for frequency tuning capability while the second capacitance is optimized for phase noise performance. This local quality differentiation allows each component to excel at its specific function without compromising the other.
3Use of energy by moving object
If power consumption is reduced, then energy efficiency is improved, but phase noise performance deteriorates
Solution Approach 1:
The patent extracts the phase noise problem from the gain stage and relocates it to the tank circuit through the second capacitance. This allows the gain stage to operate at lower power while the tank circuit handles the phase noise-critical functions, enabling low power consumption without sacrificing phase noise performance.
Solution Approach 2:
The patent introduces a second capacitance as an intermediary between the tank circuit and the output. This intermediary component allows the tank circuit to be optimized for low phase noise while the gain stage can be optimized for low power consumption, effectively mediating between the two conflicting requirements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces phase noise and maintains low power consumption, as demonstrated by a 58 GHz VCO with phase noise of -110 dBc/Hz at 1 MHz offset, outperforming other VCO designs.
Implementation Method 1
a pair of varactors coupled between the first node and the second node and configured to receive a supply signal at a supply node between the pair of varactors
Implementation Method 2
a transformer-based VCO configuration with a majority of the total capacitance coupled to the secondary stage
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
Embodiments provide a voltage controlled oscillator (VCO) having reduced single-ended capacitance. In one embodiment, the VCO may include a transformer, a capacitor bank, and a gain stage. The transformer may include a primary inductor and a secondary inductor, and the secondary inductor may be inductively coupled to the primary inductor. The capacitor bank may be coupled to the secondary inductor and may provide a majority of a total capacitance of the VCO. The gain stage may be coupled to the primary inductor and configured to receive a supply signal and to drive a differential current in the primary inductor, thereby inducing an output signal across the secondary inductor having a frequency equal to a resonant frequency of the VCO.